1. Field of the Invention
The present invention relates to a waterproof connector for a flat cable which can be mounted on the terminal portion of a flexible flat cable such as an FFC (Flexible Flat Cable) and a ribbon line.
2. Description of the Related Art
As an example of a conventional waterproof connector for a flat cable, there is known a connector shown in FIG. 7 (see Japanese Patent Publication Hei 6-5327, for example).
In FIG. 7, there are shown a male side connector and a female side connector of a waterproof connector for a flat cable. The terminal portion of a flat cable 1a with a male terminal 2a connected thereto and the terminal portion of a flat cable 1b with a female terminal 2b connected thereto are respectively stored within a male connector housing 5 and a female connector housing 6.
On the flat cables 1a, 1b, there are provided resin formed portions 3a, 3b which are respectively formed by burying the longitudinal direction partial portions of the respective cables. With the resin formed portions 3a, 3b, there are fitted ring-shaped rubber plugs 4a, 4b, respectively.
On each of the outer peripheral surfaces of the rubber plugs 4a, 4b, there are arranged two ringshaped lips. The lips of the rubber plugs 4a, 4b are closely contacted with the inner peripheral wall surface of the cable guide portion of the male connector housing 5 and the inner peripheral wall surface of the cable guide portion of the female connector housing 6 respectively, whereby the cable guide portions can be surely made waterproof.
However, in the above-mentioned conventional waterproof connector for a flat cable, for example, the flat cable 1a (by the way, this description applies similarly to the flat cable 1b as well) is only supported by the peripheral wall of the cable guide portion of the male connector housing 5 through the resin formed portion 3a and rubber plug 4a. 
For this reason, when en external force such as a tensile force is applied to the flat cable 1a, the flat cable 1a is easily displaced. Normally, the male terminal 2a is secured within the male connector housing 5 and, therefore, the displacement of the flat cable 1a applies a load to the connecting portion between the flat cable 1a and male terminal, which can raise a fear that the electrical connection of the connecting portion can be disrupted.
Further, when an external force is applied in a direction intersecting with the axial direction of the ring-shaped rubber plug 4a through the flat cable 1a, the rubber plug 4a is deformed to thereby produce a clearance between the rubber plug 4a and the inner wall surface of the cable guide portion of the male connector housing 5, which raises a fear that the waterproof condition of the cable guide portion can be worsened.
In the above-mentioned conventional waterproof connector for a flat cable, the resin of the resin formed portions 3a, 3b is charged into the uneven surfaces of the flat cables 1a, 1b to thereby prevent the formation of clearances between the resin formed portions 3a, 3b and flat cables 1a, 1b. Such resin formed portions 3a, 3b can be formed, for example, in such a manner that the flat cables 1a, 1b are held within a mold and are then insert molded. However, the productivity thereof is not high.
In view of this, there is proposed a structure in which lips similar to the lips 7a, 7b to be closely contacted with the inner periphery wall surfaces of the cable guide portions of the connector housings 5, 6 are provided on the inner peripheral surfaces of the rubber plugs 4a, 4b as well, the resin formed portions 3a, 3b are removed, and spaces between the rubber plugs 4a, 4b and flat cables 1a, 1b are kept waterproof by these lips. And, generally, it is believed that the more the number of lips is, the higher the waterproof condition is.
However, for example, as in the rubber plugs 4a, 4b, when two lips are formed on the inner peripheral surface of a ring-shaped seal member to be formed by injection molding, there is formed a constricted portion in a mold for injection molding. And, when the two lips are formed so as to be closely contacted with the outer peripheral surface of a flat cable having a small thickness, there is a fear that the strength of the constricted portion of the mold can be lowered.
That is, as shown in FIG. 6, in a mold 8, there are formed two ring-shaped cavities 9 into which molten injection molding material is filled to provide two ring-shaped lips. In the portions of the mold that are surrounded by the respective cavities 9, there are produced constricted portions; and, the mold 8 is divided into a set of mold pieces 8a, 8b in a plane passing through the centers of the two ring-shaped cavities 9. Therefore, there are produced constricted portions in both pieces 8a, 8b as well. Here, since the thickness of the flat cable is small, the opposing clearance between the cavities 9 is small, so that the thickness W of the constricted portion is small, which raises a fear that the strength of the constricted portions of the two mold pieces can be lowered. And, there is a feat that the lowered strength of the mold pieces constituting the mold can lower the productivity of the seal members and thus can lower the productivity of the connector.